The expert survey method often referred to as Delphi analysis was developed at Rand Corporation [link] in the 1950s. Since then, it has been widely used in technological, economical, and social foresight, as well as in decision support processes, especially in the context of choice problems with multiple conflicting criteria. The essence of the online Delphi method is multiple round interviews of an expert group who answer questions in a structured e-survey and verify hypotheses called Delphi statements or questions. These can be defined by the client contracting the study or the core experts employed by the Delphi supplier, usually a consulting or research institution. Delphi studies are often interdisciplinary. For example, in technological foresight, economic, environmental and social conditions are also examined. Therefore, the surveys are usually subdivided into separate research areas, hereinafter referred as "survey sections". Usually, each survey section corresponds to an appropriate thematic panel of experts.

A standard Delphi survey questionnaire comprises of 20-200 questions subdivided into thematic sections. Each section usually contains 10-30 questions, which cover technological, economic and sociological problems or hypotheses. Each question is associated with a specific trend, event, technological or investment priority, market expansion direction, etc. Respondents can select sections or questions which correspond to their particular area of expertise. If an expert is not able to reply a question, it is possible to select the option "no opinion" and move on to another question. A characteristic feature of the Delphi method is its multi-round knowledge elicitation process, in most cases two or three rounds. Subsequent rounds contain the same, modified or extended questions, based on the results of the previous round. The aims of this procedure are listed below:

• Verification of results obtained in the previous rounds by making them available to experts responding to the same or similar questions. This is designed to facilitate a response mainly to questions which were ambiguously answered. In the case of questions with quantitative responses, this procedure aims to reduce standard deviations of previous-round replies.
• Clarification of replies with detailed questions that refer to particular aspects of previous-round questions, by asking for justification of particular responses, and showing the causes of identified trends or events.
• Including questions that complete or update the question set used during the previous round.

The credibility of subsequent rounds can be increased by filtering the group of experts so that the least reliable respondents do not continue to participate in the survey. After the final round, a panel discussion is often organized to validate the results.

The overall survey process can be greatly facilitated by using an interactive application to provide replies. Computer supported Delphi appeared relatively early in the digital era, in the 1970s. Chapter 7 in [link] . With the development of the Internet, email and web-based surveys almost completely replaced traditional paperwork. Due to the increasingly complex structure of surveys, including contingent questions, filling in a questionnaire sent as a file would significantly complicate further statistical analysis of the results. Therefore, specialized survey applications should be used.

Further information on the Delphi research method is included in the classic monograph edited by Linstone and Turoff [link], while information about applications and implementations of the online surveys can be found e.g. in [link] or [link]. The implementations of foresight support systems, including Delphi surveys, are discussed in a series of articles, cf. e.g. [link],[link] and [link]. For a discussion of the role of the Delphi method in decision support and forecasting, the reader can refer to the publications listed here